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77 Bio 103 Nervous System Lecture Outline: NERVOUS SYSTEM
[Chapters 10, 11, 12]
Introduction
Neural Tissue Types:
Neurons –
Neuroglial Cells Divisions
1. Central Nervous System (CNS)
Parts:
Functions: analyze, evaluate, integrate 
2. Peripheral Nervous System (PNS)
Nerves:
A. Divisions of PNS
1. Sensory Division (afferent)
Receptors –
2. Motor Division (efferent)
Effectors –
Motor Division consists of:
Somatic –
Autonomic –
B. Nervous System Functions
Sensory Function:
-
Integrative Function
-
78 Bio 103 Nervous System Motor Function
-
The Neuron
Neurons are specialized to react to chemical and physical changes in their
surrounds and conduct impulses in response to these changes
A. Structures of the Neuron
1. Cell body (soma)
- perikaryon
- Nissl bodies
*
2. Dendrites
3. Axon
- ends at synaptic terminal
- initial segment:
- axon hillock:
Myelination of Axons
White matter
Gray matter
-
79 Bio 103 Nervous System B. Classification of Neurons
1. Structure
- based on number of cytoplasmic extensions
a. Bipolar neurons
b. Unipolar neurons
c. Multipolar neurons
-
2. Function
- based on function
a. Sensory neurons
- afferent
- carry impulses to CNS
b. Interneurons
- link neurons
c. Motor neurons
- carry impulses away from CNS
- carry impulses to effectors
-
Neuroglial Cells
A. PNS neuroglia
1. Schwann Cells
- produce myelin found on peripheral myelinated neurons
-
80 Bio 103 Nervous System 2. Satellite Cells
- support clusters of neurons cell bodies (ganglia)
B. CNS neuroglia
1. Astrocytes
- regulates ion concentration
- connect neurons to blood vessels
2. Oligodendrocytes
- provides myelin for many axons
3. Microglia
- proliferate where brain or spinal cord is injured to diseased
4. Ependyma
- ciliated
- line central canal of spinal cord
C. Neural Response to Injury
*
1. Macrophages remove fragments of myelin and other cellular
debris
2. Neuroglial cells secrete __________
3. Axon is stimulated to develop a sprout which may grow into a
tube formed by connective tissue
4. Schwann cells proliferate and _______
81 Bio 103 Nervous System The Synapse:
* nerve impulses pass form neuron to another cell at the synapse
- presynaptic cell
- postsynaptic cell
neuro-neuronal junction:
NMJ:
neuroglandular junction:
Synaptic transmission:
-
Neurophysiology
A. Transmembrane potential
1. Passive forces:
Chemical gradients:
ECF
ICF
Electrical gradients:
Positive charge
Negative charge
Resting membrane potential = -70 mV
- due to
2. Active forces:
Sodium-Potassium exchange pump
- exchange of 3 Na+ for every 2 K+
[ moves 3 Na+ out of the cell; moves 2 K+ into the cell;
uses ATP as energy source to move these ions]
- used to maintain the resting potential (______)
82 Bio 103 Nervous System B. Local Potential Changes
Caused by:
* environmental changes affect the membrane potential by
opening a gated ion channel
Graded (or local) Potentials
- do not spread far from site of stimulus
Threshold stimulus
- a local potential that is strong enough to start an action potential
Depolarization Hyperpolarization Repolarization -
C. Action Potentials
1. At rest the membrane is ____________
2. Threshold stimulus is reached
3. Sodium channels ______ and membrane ____________
4. Potassium leaves cytoplasm and membrane ______________
D. All-or-None Response
If a neuron responds at all, it responds completely
A nerve impulse is conducted whenever a stimulus of threshold
Intensity or above is applied to an axon
All impulses carried on an axon are the _______________
E. Refractory Period
1. Absolute –
2. Relative -
83 Bio 103 Nervous System F. Na+/ K+ exchange pump
Over time this pump will return ions to their prestimulation levels
on appropriate side of membrane
Na+  ______ are pumped _______ of the cell
K+  ______ are pumped _______ the cell
G. Propagation (or conduction) of AP
1. Continuous propagation:
- chain reaction that spread AP along every part of the cell
membrane
- occurs on _________________
- 1m/sec
2. Saltatory propagation:
- jumping of AP from ________ to __________ in myelinated
fibers
H. Axon Diameter
1. Type A fibers
2. Type B fibers
3. Type C fibers
Neurotransmitters
Synaptic transmission: Chemical Synapses
presynaptic neuron ---> synaptic cleft ---> postsynaptic neuron
Neurotransmitters can be excitatory or inhibitory
E
I
84 Bio 103 Nervous System Acetylcholine (ACh)
Norepinephrine (NE)
- adrenergic synapses
- released at most SNS post-ganglionic fibers
Dopamine
Serotonin
- not enough may cause depression
- SSRI
GABA (gamma aminobutyric acid)
- inhibitory
-
Neuromodulators:
Endorphins -
Impulse Processing
The way the nervous system processes impulses and acts upon them
Neural Pools
- groups of interneurons that make synaptic connections
with each other
- interneurons work together to perform a common function
- each pool receives input from other neurons
- each pool generates output to other neurons
Convergence
- neuron receives input from ____________
- incoming impulses represent information from different
types of sensory receptors
- allows nervous system to collect, process, and respond
to info
- makes it possible for a neuron to sum impulses from
different sources
85 Bio 103 Nervous System Divergence
- one neuron sends impulses to __________
- can amplify an impulse
- impulse from a single neuron in CNS may be amplified to
activate enough motor units needed for muscle
contraction
Nervous System Structure
1. PNS =
Nerves Ganglia –
2. CNS =
Tract (column) Nucleus (center) A. Meninges
- Membranes surrounding ___________
- 3 Layers:
1. Dura mater
2. Arachnoid mater
3. Pia mater
Organization of the spinal meninges:
Epidural space
Dura mater
Arachnoid
Subarachnoid space
Pia mater
86 Bio 103 Nervous System B. Ventricles
1. Interconnected cavities within cerebral hemispheres and brain
stem
2. Continuous with central canal of spinal cord
3.
Lateral ventricles
Third ventricle
Fourth ventricle
Cerebral aqueduct
C. Cerebrospinal Fluid
- Secreted by choroid plexus (__________)
- Circulates in ventricles, central canal of the spinal column, and
subarachnoid space
- clear liquid that provides ____________ and ____________
- helps maintain stable ion concentrations in CNS
Hydrocephalus:
- blocked _______________
- excess production of CSF
- treatment: hydrocephalic shunt
D. Spinal Cord
1. Slender column of nervous tissue continuous with the brain
2. Extends downward through vertebral canal
3.
Functions:
- center for spinal reflexes
- conduit for nerve impulses to and from the brain
Tracts:
- ascending tracts –
- descending tracts –
87 Bio 103 Nervous System Reflex arcs:
Reflexes – automatic, subconscious responses to stimuli
within or outside the body
Pathway:
Receptor
Afferent (sensory) neuron
CNS
Efferent (motor) neuron
Effector
Reflex Behavior:
Patellar reflex
-
Withdrawal reflex
-
Brain
Functions:
- interprets sensations
- determines perception
- stores memory
- reasoning
- make decisions
- coordinates muscular movements
- regulates visceral activities
- determines personality
88 Bio 103 Nervous System Major Parts of the brain:
A. Structure of Cerebrum
1. corpus callosum connects cerebral hemispheres (left and
right)
2.
3.
4. longitudinal fissure –
5. transverse fissure separates cerebrum from cerebellum
B. Functions of the Cerebrum
- interpreting impulses
- initiating voluntary movements
- storing information as memory
- retrieving stored information
- reasoning
- seat of intelligence and personality
C. / D. Lobes of Cerebral Hemispheres and Functions
1. Frontal
2.
3. Temporal
4.
89 Bio 103 Nervous System E. Functional Regions of Cerebral Cortex
Cerebral cortex – thin layer of gray matter that constitutes
the outermost portion of cerebrum
1. Sensory Areas
Cutaneous Area
Visual Area
Auditory Area
Area for Taste
Area for Smell
2. Association Areas
- regions that are not primary motor or sensory areas
- widespread throughout the cerebral cortex
- analyze and interpret sensory experiences
Frontal Lobe Association Areas:
Parietal Lobe Association Areas:
Temporal Lobe Association Areas:
Occipital Lobe Association Areas:
-
90 Bio 103 Nervous System Memory (association area)
Short Term
- working memory
- closed neuronal circuit
- circuit is stimulated over and over
Long Term
- changes structure of function of neurons
- enhances synaptic transmission
3. Motor Areas
Primary Motor Areas:
Broca’s Area:
Frontal Eye Field
F. Basal Nuclei
- masses of gray matter
- deep within cerebral hemispheres
- produce ___________
- control certain muscular activities primarily by inhibiting
motor functions
G. Diencephalon
- Area between cerebral hemispheres and above the
brainstem
- Surrounds third ventricle
- Includes: thalamus, hypothalamus, _____________, optic
chiasma, Infundibulum, posterior pituitary, Mammillary
bodies, and _____________
91 Bio 103 Nervous System Thalamus
- gateway for sensory impulses heading to cerebral
cortex
- channels impulses to appropriate part of cerebral
cortex for interpretation
Hypothalamus
- maintains homeostasis by regulating visceral
activities
H. Brain Stem
3 Parts:
1.
- contains bundles of fibers that join lower parts of
brainstem and spinal cord with higher part of
brain
- cerebral aqueduct
- corpora quadrigemina –
2.
- rounded bulge on underside of brainstem
- relays nerve impulses to and from medulla
oblongata and cerebellum
3.
- conducts ascending and descending impulses
between brain and spinal cord
- contains cardiac, vasomotor, and respiratory control
centers
- contains various non-vital reflex control centers
92 Bio 103 Nervous System I. Cerebellum
- inferior to occipital lobes, posterior to pons and medulla
oblongata
- cerebellar cortex –
- arbor vitae –
- integrates sensory information concerning position of body
parts
A. Peripheral Nervous System (PNS)
1.
-
somatic fibers connecting to the skin and skeletal
muscles
autonomic fibers connecting to viscera
2.
-
somatic fibers connecting to the skin and skeletal
muscles
autonomic fibers connecting to viscera
B. Structure of Peripheral Nerve
Connective tissue coverings:
Epineurium –
Perineurium –
Endoneurium –
C. Nerve Fiber Classification
1. ___________________ (afferent) conduct impulses into brain or
spinal cord
General visceral afferent fibers – carry sensory impulses to CNS
from blood vessels and internal organs
General somatic afferent fibers – carry sensory impulses to CNS
from skin and skeletal muscles
2. ___________________ (efferent) conduct impulses to muscles
or glands
93 Bio 103 Nervous System General somatic efferent fibers – carry motor impulses from CNS to
skeletal muscles
General visceral efferent fibers – carry motor impulses away from
CNS to smooth muscles and glands
3. Mixed Nerves – contain both ___________ nerve fibers and
___________ nerve fibers
Special somatic efferent fibers
- carry motor impulses from brain to muscles used in
chewing, swallowing, speaking, and forming facial
expressions
Special visceral afferent fibers
- carry sensory impulses to brain from olfactory and taste
receptors
Special somatic afferent fibers
- carry sensory impulses to brain from receptors of sight,
hearing, and equilibrium
94 Bio 103 Nervous System D. Cranial Nerves - 12 Pair
Name
Major Function
I. OLFACTORY
S only: Smell
II. OPTIC
S only: Sight
III. OCULOMOTOR
S: Receptors that influence pupil size
M: Muscles that move eye
(except sup. oblique, lat. rectus)
IV. TROCHLEAR
S: Muscle sense (eye muscles)
M: Superior oblique eye muscle
V. TRIGEMINAL
S: Sensations of head, face
M: Muscles of mastication
VI. ABDUCENS
S: Muscle sense (eye muscles)
M: Lateral rectus eye muscle
VII. FACIAL
S: Tastebuds (anterior 2/3 tongue)
M: Muscles for facial expressions
VIII. VESTIBULOCOCHLEAR
(or AUDITORY)
S only: Sense of balance, hearing
IX. GLOSSOPHARYNGEAL
S: Tastebuds (posterior 1/3 tongue)
Detects BP in the carotid arteries
M: Muscles for swallowing
X. VAGUS
S: Pharynx, thoracic & abdominal
viscera
M: Major PSN nerve to thoracic &
abdominal viscera
XI. ACCESSORY (SPINAL)
S: Proprioception from head, neck,
shoulder muscles
M: Head and shoulder movements
XII. HYPOGLOSSAL
S: Proprioception from tongue
M: Tongue movement and swallowing
S = sensory function
M = motor function
95 Bio 103 Nervous System E. Spinal nerves
* Mixed nerves
31 pairs exit through intervertebral foramina
8 pr. cervical nerves
12 pr. thoracic nerves
5 pr. lumbar nerves
5 pr. sacral nerves
1 pr. coccygeal nerves
_______________
31 pair spinal nerves
Dorsal Root (posterior or sensory root)
- axons of sensory neurons
Dorsal root ganglion
- cell bodies of sensory neurons whose axons conduct
impulses inward from peripheral body parts
Ventral root (anterior or motor root)
- axons of motor neurons whose cell bodies are in spinal
cord
Spinal Nerve – union of ventral and dorsal roots
Nerve Plexus – complex networks formed by anterior branches of
spinal nerves
- fibers of various spinal nerves are sorted and recombined
1. Cervical Plexuses
(C1 - C5)
C1 – C4 lies deep in the neck
- supplies muscles and skin of the ____________
C3 – C5 contribute to the _______________
96 Bio 103 Nervous System 2. Brachial Plexuses
C5 - T1 - innervates shoulder / upper arm
Musculocutaneous nerve – muscles of the anterior
arms and skin of forearms
Ulnar and Median nerves – supply muscles of
forearms and hands
Radial nerve – supply posterior muscles of arms and
skin of forearms and hands
Axillary nerve – supply muscles and skin of anterior,
lateral, and posterior arms
3. Lumbosacral Plexuses
T12 – S5
- extends from lumbar region into pelvic cavity
Obturator nerve – supply motor impulses to adductors
of thighs
Femoral nerve – supply motor impulses to muscles of
anterior thigh and sensory impulses from skin
of thigh and legs
Sciatic nerve – supply muscles and kin of thighs, legs,
feet
A. Autonomic Nervous System (ANS)
- functions without conscious effort
- controls visceral activities
- regulates –
Two Divisions:
1. Sympathetic (SNS) - strongly stimulated by stress 
2. Parasympathetic (PSN) - Rest and repose
-
97 Bio 103 Nervous System SNS Stimulation Responses:
- Dilates pupils
- Contracts arrector pili muscles
- VC vessels in skin and viscera
- Dilates vessels in skeletal and cardiac muscles
-
Secretion of epinephrine
Glucose is released from liver into blood
Dilation of bronchioles
PSN Stimulation Reponses:
- Elimination of waste
- Increases digestive activity
-
Relaxation of bladder sphincters
-
Dilates vessels to external genitalia
Control of Autonomic Activity
- Controlled largely by CNS
-
Medulla oblongata regulates –
-
Hypothalamus regulates –
-
Limbic system and cerebral cortex control emotional
responses
98 Bio 103 Nervous System Life Span Changes
- Brain cells begin to die before birth
-
Over average lifetime, brain shrinks 10%
-
By age 90, frontal cortex has lost half its neurons
-
Number of dendritic branches decreases
-
Decreased levels of neurotransmitters
-
Slowed responses and reflexes
-
Changes in sleep patterns that result in fewer sleeping
hours
Clinical Applications: Cerebral Injuries and Abnormalities
Concussion
Cerebrovascular Accident
Cerebral Palsy
Parkinson’s Disease